(1) Field of the Invention
The present invention relates generally to an apparatus and method for navigating a vehicle using GPS.
(2) Description of the Background Art
Recently, various types of route guiding systems for vehicles have been proposed with which to correct accumulated movement errors relative to a starting point using a gyroscope, a GPS (Global Positioning System) is utilized.
One of various types of GPS navigation systems has been proposed in which a single GPS antenna is installed on a roof top of a vehicle body and the present position of the vehicle is calculated on the basis of electromagnetic waves derived from a plurality of satellites by the GPS antenna.
For accurate GPS positioning three satellites are required for two dimensional positional calculation and four are needed for three-dimensional positional calculation. The reason that the antenna is installed to pick up electromagnetic waves as far away as possible with a wide field of view.
In addition, a plurality of GPS antennae may be installed on different positions of the vehicle and a diversity method adopted in which the present position of the vehicle is calculated on the basis of electromagnetic input from the antennae having the highest reception sensitivity.
However, since, in the system described above, the GPS antennae are installed on the roof top of the vehicle, major modification to the vehicle body is required in order to counter water leakage and provide a sufficiently rigid roof structure. Consequently, a specialized vehicle body structure is required and the cost of implementing the GPS navigating system becomes high.
Additionally, in the diversity method described above, antennae having high reception sensitivities are used, and measurement of position on the basis of actual reception results is carried out. In many cases, a long time may be required to receive electromagnetic waves from the satellites and calculate the present position of the vehicle and a great number of opportunities for measuring position may not occur due to an insufficient number of satellites. Therefore, lack of practicability becomes a drawback.